Large-scale power generators often use gas turbine engines to supply power to a geographic region. Reliable start up of these engines is critical to ensure that power outages do not occur.
Electric starters are known for starting small engines, but the special requirements of large engines have generally made them inappropriate for use with large engines. Many gas turbines in the 20 to 50 MW range are derivatives of aircraft engines (known as “aeroderivatives” and, as such, they initially retained the lightweight, high-performance pneumatic starters from the initial design. As applications evolved, the pneumatic starters were replaced with hydraulic starters because weight is less of a concern in ground-based gas turbine engines. The next logical step is to apply electric motors to replace the hydraulic starter units.
One of the challenges in designing electric starters is to create a high-performance unit with minimal (packaging) size and total weight. Out of the currently available electric starter technology (i.e., induction, switched reluctance, permanent magnet), permanent magnet motors offer the highest performance density.
More particularly, electric starters rely on electric motors to convert electrical input power into mechanical power in the form of torque and rotation, which in turn is used to start an engine. All electric motors are prone to common failure modes, such as broken or shorted wires. However, despite their high performance density, permanent magnet motors are also prone to performance degradation resulting from demagnetization of the magnets due to, for example, excessive environmental temperatures. In any case, the power delivered by the permanent magnet motor may drop to zero or to a very low level, depending on the severity of the damage. Depending on the degree of failure, many of these degradations are not detectable and may result in operational failures or, in extreme cases, generation of excessive heat that may ignite or melt the starter components.
There is a desire for a system and method that can detect performance degradation in a permanent magnet-based electric starter.